Handling of fluoboric acid



Patented Feb. 5, 1952 HANDLING OF FLUOBORIC ACID Jerome W. Sprauer, Niagara Falls, N. Y., and Oliver S. Sprout, Jr., North Hills, Pa., assignors to The Pennsylvania Salt Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Application May 14, 1949, Serial No. 93,432

9 Claims.

This invention relates to the handling of concentrated solutions of .fiuoboric acid and more particularly to containers in which such solutions may be shipped or stored for an extended period of time.

It has heretofore been the practice when storing or shipping fiuoboric acid to use glass containers or containers lined with a suitably resistant organic material such as parafl'in wax. Glass containers are objectionable due to their structural limitations, special precautions being necessary to protect the containers from damage. Wax lined containers are objectionable since the protective surface coating of Wax is relatively soft and can be easily damaged, with the result that the metal or other material from which the container is made is exposed to attack by the acid.

As increasingly concentrated solutions of fluoboric acid were prepared for commercial use, the problem of suitable containers for the concentrated solutions became more acute. The glass which was fairly resistant to weaker solutions of fiuoboric acid was found to be sufficiently attacked by solutions having a concentration of over 40% to render its use as a container material unsatisfactory, particularly in view of its structural limitations.

Numerous materials were tested in an attempt to find one which would be satisfactory for forming containers for concentrated solution of fluoboric acid. Some of these materials were lead, nickel, stainless steel, copper, monel metal and glass, none of which proved entirely satisfactory.

We have now discovered that aluminum metal is a particularly satisfactory material from which to make containers for more concentrated solutions of fiuoboric acid since aluminum shows substantially no attack by fluoboric acid concentrations of over 65% and such slight attack with concentrations of 60% that aluminum containers can satisfactorily be used. for storing and handling such acids. This resistance of aluminum to attack by concentrated solutions of fluoboric acid includes concentrations up to 100% even though the fluoboric acid may be dissociated at the higher concentrations into hydrogen fluoride and boron trifluoride in accordance with the equation HBF4 )HF+BF3. Also other materials which do not seriously attack aluminum may be present together with the fluoboric acid as long as the ratio of water to HBF4 does not exceed 2 parts water to 3 parts HBF4 by weight, it being understood that i'luoboric acid as used in the claims includes I-IBF4 alone or together with such materials.

This superior resistance of aluminum to attack by concentrated solutions of fluoboric acid is surprising in view of the fact that aluminum is readily attacked by weaker concentrations of such acid and even by concentrations as high as 45%. The resistance exhibited by aluminum is surprising, further, in that magnesium is rapidly attacked by all concentrations, including '70% solution of fluoboric acid. In fact, the observed susceptibility of metals, generally, to attack by fluoboric acid turned the search for materials of construction in other directions and the surprising resistance of aluminum to strong fiuoboroc acid was noted accidentally in connection with other work.

Aluminum metal has the necessary strength to permit its use as a container without the necessity of reinforcing the container by some other metal. Aluminum is also exceptionally light when compared with most structural metals. These factors together with its high resistance to corrosion by concentrated solutions of fluoboric acid make the metal ideal for constructing shipping containers or storage vessels which must be handled and shipped as freight.

The resistance of aluminum as compared with some of the other materials tried is readily apparent on reference to the following tables in which the resistance values are given in I. P. Y.

-(inches penetration per year):

9 Table I (Acid: 72.6% HBFi, 5.09% H3BO3. Test: 3-0 days, room temperature) I. P. Y. Copper 0.0033 Nickel 0.0020 Glass (Soda lime) 0.1928

Table II (Acid: 72.6% HBF4, 5.09% H3303. Test: 10 days, room temperature) I. P. Y. Silver 0.00041 Pyrex glass 0.124

Table III (Acid: 64.2% HBF4, 7.09% H3BO3. Test: 32 days,

room temperature) concentrations of fluoboric acid can readily be shown by tests involving merely immersing a sheet of aluminum in acids of the concentration, its resistance to which is being tested.

Example 1 A 3 /6" length of aluminum, by having a purity of 99.79% was immersed in a 70.89% solution of fluobcric acid containing 5.20% boric acid. The length of the portion immersed in the acid was 1 inches. This gave a total area exposed to the acid, considering the two sides, two edges and one end, of 1.11 square inches. The sample was stored with the acid, as above described, in a waxed test tube under laboratory conditions at room temperature.

The test was continued for 30 days. During this time, the test strip of aluminum was periodically removed to determine any evidence of action by the acid thereon. After 9 days no visible evidence of corrosion was observed. After 16 days the test strip appeared possibly a little more shiny than when originally immersed in the acid. After 30 days of immersion no appreciable evidence of attack was noted. There was no line of demarkation between the exposed and unexposed portion of the aluminum strip. The only evidence of possible attack was that in some areas of the immersed portion there was a slightly tarnished appearance.

The aluminum test strip was carefully weighed before immersion and after immersion in the acid for the 30'day period. At the end of this time the total loss in weight was 0.0003 gram. A calculation of the inches penetration per year for the aluminum gave a value 0.0000743.

Example 2 A 4 length of aluminum, 2 by 5" was immersed in a testing acid analyzing 72.5% fiuoboric acid and 7.8% boric acid. The total length immersed in the acid was 2 inches, the test as in Example 1 was continued for 30 days. However, the temperature of the acid and sample was maintained at 100 F. by storage in a room of this temperature throughout the 30 da period. After this time the test strip was removed from the acid solution and carefully examined. There was no evidence of any action except for a small very faintly tarnished spot on the strip where it was exposed to the gas phase, that is, the portion of the strip not immersed in the acid and not protected by clamping means. No coloring of the acid was observed. The total loss in weight at the end of the 30 day period was found to be 0.0021 gram. On calculation this gave an I. P. Y. value of 0.00016. When it is considered that this test was carried out at a temperature of 100 F., the I. P. Y. value obtained is exceptionally good.

In describing our invention the word container is used to define structural apparatus adapted for the handling and storing of fluoboric acid. It is apparent that every part of such container need not be made of aluminum in order to practice the invention and obtain the benefits thereof since a portion of the container could be made of some relatively expensive alloy or plastic which was resistant to attack by concentrated solutions of fluoboric acid while the remainder of the container could be made of aluminum to reduce the over all weight or cost of the container. It is, therefore, understood that wherever aluminum container or a like phrase is used in the body of the specification and in the claims it is intended to include those structures in which only a portion of the metal, adapted to contact the fluoboric acid, is formed of aluminum.

Having thus described our invention, we claim:

1. A package of fiuoboric acid comprising an aluminum container and a solution of fiuoboric acid therein, the concentration of I-IBF4 being not less than 60%.

2. A package of fluoboric acid comprising an aluminum container and a solution of fluoboric acid therein, the concentration of IIBF; being not less than 65%.

3. In combination, an aluminum container and fluoboric acid therein, said acid containing less than 2 parts water per 3 parts HBF4 by weight.

4. In combination, an aluminum container and fiuoboric acid therein, said acid containing less than 35 parts by weight of water for every 65 parts by weight of I-IBF4.

5. A package of fluoboric acid comprising an aluminum container and fiuoboric acid, HBF4 being present together with hydrogen fluoride and boron trifluoride and the acid containing less than 40% water.

6. A package of fiuoboric acid comprising an aluminum container and a solution of fiuoboric acid having a small amount of boric acid therein, the concentration of I-IBF4 being greater than 60%.

7. A method of shipping and storing concentrated solutions of fluoboric acid in which the HBF4 concentration is greater than 60% comprising containing said acid solutions in an aluminum container.

8. A method of shipping and storing concen trated solutions of fluoboric acid in which the HBF4 concentration is greater than 65% comprising containing said acid solutions in an aluminum container.

9. A fluoboric acid package comprising an aluminum container and a solution of fluoboric acid said fluoboric acid solution including 65 to HBF'4 and 3 to 10% of boric acid.

JEROME W. SPRAUER. OLIVERS. SPROUT, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,701,937 Wilkinson et al. Feb. 12, 1929 FOREIGN PATENTS Number Country Date 13,137 Great Britain 1911 

3. IN COMBINATION, AN ALUMINUM CONTAINER AND FLUOBORIC ACID THEREIN, SAID ACID CONTAINING LESS THAN 3 PARTS WATER PER 3 PARTS HBF4 BY WEIGHT. 